Ullyn Thonwyr is a Prince of Summerlund of the noble house of Thonwyr. His father is the current King of Summerlund, Hadyn Thonwyr, and his mother is Eleanor Kassryx, the current Queen. His older brother, Harbryn is Duke of Estshar and Crown Prince of Summerlund. His younger sister is Princess Shairi.
As a middle child, Ullyn is more of a scholar and poet than his older brother. He is well-liked by the people of Summerlund for his gentle ways, and he is quite loyal to his older brother. Unlike his dark-haired older brother, he has red hair like his sister, an inheritance from the days when House Kassryx intermarried with some of the elves of Faerinwold.